SketchUp flip not aligned with construction lines

Hi, I’m a beginner in SketchUp. I am creating the model of a twin apartment. While trying to flip the model, the result didn’t align with the construction line of the initial model…
How do I solve it? Thanks.

Flip along acts along the direction of a main model axis or a group or component’s internal axis. Those don’t necessarily have any relation to a construction line.

I imagine you will want to use a different means of mirroring. You could use Scale set to -1, for example. There are also mirroring extensions you can use.